Rubbish DNA: The functionless fraction of the human genome

TL;DR

This paper reviews the concept of nonfunctional 'rubbish' DNA in the human genome, discussing its origins, evolutionary maintenance, and methods to estimate its proportion, highlighting that most of the genome is likely nonfunctional.

Contribution

It provides a comprehensive review of the concepts, evidence, and methodologies related to the functional and nonfunctional parts of the human genome from an evolutionary perspective.

Findings

Most of the human genome is nonfunctional junk DNA.

Various methods estimate a small fraction of the genome is functional.

Recent estimates suggest a limited portion of the genome has biological function.

Abstract

Because genomes are products of natural processes rather than intelligent design, all genomes contain functional and nonfunctional parts. The fraction of the genome that has no biological function is called rubbish DNA. Rubbish DNA consists of junk DNA, i.e., the fraction of the genome on which selection does not operate, and garbage DNA, i.e., sequences that lower the fitness of the organism, but exist in the genome because purifying selection is neither omnipotent nor instantaneous. In this chapter, I (1) review the concepts of genomic function and functionlessness from an evolutionary perspective, (2) present a precise nomenclature of genomic function, (3) discuss the evidence for the existence of vast quantities of junk DNA within the human genome, (4) discuss the mutational mechanisms responsible for generating junk DNA, (5) spell out the necessary evolutionary conditions for maintaining junk DNA, (6) outline various methodologies for estimating the functional fraction within the genome, and (7) present a recent estimate for the functional fraction of our genome.